The present invention relates to a continuous method for producing 1,4-dioxane.
There are a variety of methods known for the continuous preparation of 1,4-dioxane. The most widely employed commercial methods for the continuous preparation of 1,4-dioxane consists of dehydrating ethylene glycol, a polyethylene glycol, a mixture of ethylene glycol and one or more polyethylene glycol(s) or a mixture of polyethylene glycols in the presence of a sulfuric acid catalyst. The dehydration reaction is conducted at an elevated temperature, usually above 170.degree. C. and at atmospheric pressure. The reaction product which consists of 1-4 dioxane, water and by-products is continuously removed from the reaction mixture as an overhead product, condensed and the 1,4-dioxane subsequently separated from the water and by-products. As the 1,4-dioxane is removed from the reactor and the sulfuric acid is deactivated, additional amounts of the glycol(s) and sulfuric acid are added to the reactor. Unfortunately, severe charring and the formation of tars are inherent in the sulfuric acid catalyzed method for preparing 1,4-dioxane, which results in losses in product yield. In addition, foaming in the reactor causes the tars to be carried over into the product, thereby causing discoloration of the reaction product. The formation of tar and its subsequent carry-over into the product require the vessels and equipment used in the process to be cleaned on a frequent basis.
In an alternative method for producing 1,4-dioxane, German Offenlegungschriften Nos. 2,430,355 and 2,300,990 describe dehydrating polyethylene glycol to 1,4-dioxane using a solid cation exchange resin as the dehydration catalyst. The reaction is conducted at an elevated temperature below 170.degree. C. and a sub-atmospheric pressure to increase the rate of dioxane distillation. Unfortunately, the ion exchange resins are inherently unstable at the reaction temperatures employed. In addition, the handling difficulties associated with a solid/liquid reaction system lead to increased operating costs and capital investment.
U.S. Pat. No. 3,825,568 discloses yet another method for the production of 1,4-dioxane. In the described method, ethylene oxide is dimerized in the presence of SiF.sub.4 or BF.sub.3 or the adduct formed from BF.sub.3 and 1,4-dioxane in the liquid phase at temperatures from -50.degree. C. to 0.degree. C. and at an atmospheric pressure or a pressure greater than atmospheric pressure. Due to their corrosive and other undesirable properties, compounds such as BF.sub.3 and SiF.sub.4 require special handling.
In view of the stated deficiencies, it would be advantageous to develop a process for the preparation of 1,4-dioxane which does not exhibit the deficiencies of the prior art processes.